Neisseria meningitidis is a Gram-negative encapsulated bacterium which colonises the upper respiratory tract of approximately 10% of human population. Although polysaccharide and conjugate vaccines are available against serogroups A, C, W135 and Y, this approach cannot be applied to serogroup B because the capsular polysaccharide is a polymer of polysialic acid, which is a self antigen in humans. To develop a vaccine against serogroup B, surface-exposed proteins contained in outer membrane vesicles (OMVs) have been used. These vaccines elicit serum bactericidal antibody responses and protect against disease, but they fail to induce cross-strain protection [1]. Some workers are therefore focusing on specific meningococcal antigens for use in vaccines [2].
One such antigen is ‘NMB1870’. This protein was originally disclosed as protein ‘741’ from strain MC58 [SEQ IDs 2535 & 2536 in ref. 3; SEQ ID 1 herein], and has also been referred to as ‘GNA1870’ [refs. 4-6, following ref. 2] and as ‘ORF2086’ [7-9]. This lipoprotein is expressed across all meningococcal serogroups and has been found in multiple meningococcal strains. NMB1870 sequences have been grouped into three families (referred to herein as families I, II & III), and it has been found that serum raised against a given family is bactericidal within the same family, but is not active against strains which express one of the other two families i.e. there is intra-family cross-protection, but not inter-family cross-protection.
To achieve cross-strain protection using NMB1870, therefore, more than one family is used. To avoid the need to express and purify separate proteins, it has been proposed to express different families as hybrid proteins [10-12], including two or three of the families in a single polypeptide chain. Several hybrids have been tested and give encouraging anti-meningococcal efficacy.
It is an object of the invention to provide further and improved approaches for overcoming the family specificity of protection afforded by NMB1870, and to use these approaches for providing immunity against meningococcal disease and/or infection, particularly for serogroup B.